There are a number of important needs and uses for improved strong, hard, tough materials capable of being fabricated under feasible conditions and withstanding extremely severe conditions of use. For a great many such purposes, there are existing materials which do a reasonably good or in some instances an extremely good job, but for some other purposes, there simply are not suitable materials available. For a number of purposes where inherent chemical resistance is an important requirement, there is a very definite need for improved materials having the combination of properties including extreme hardness and toughness as well as chemical stability at very high temperatures. For example, in die casting operations and other hot forming operations, particularly with certain metals and other materials which are cast or extruded at extremely high temperature, it has been virtually impossible to find satisfactory tooling materials. Some of the products handled in operations of this sort are extremely difficult to handle because of their high temperature fabrication conditions and because of the abrasive nature of the products themselves. For example, extrusion of stainless steel and titanium using steel tooling such as dies results in excessive wear of such components, use of ceramic materials such as hot pressed SiC and Si.sub.3 N.sub.4 eliminates the wear problem, but such components fail by brittle fracture induced in part by a lack of toughness.
At the present time, products such as silicon carbide and silicon nitride and aluminum oxides are being used for a number of these purposes or are at least of interest for possible use. Such materials, however, have certain limitations and usually are deficient either in toughness or in hardness or in high temperature stability.